Anyway, apart from being more secure than IE, Firefox has a wonderful system for extensions. I use a few to make working with it nicer adding features such as remembering your open tabs and reopening them automatically when you start up, backing up / synchronising bookmarks between machines, a weatherforecast feed onto a menu bar, etc..
The one that may be of most relevance here though is the Web Developer one. This adds a new menu bar with a whole range of useful options on it. As a few examples how about:
- Find broken images
- View cookie information
- Clear http authentication
- Outline table cells
- Switch the size to standard or custom sizes (800x600, or etc.)
- Validate HTML, CSS, etc.